The goal of this proposal is to elucidate the role of the p42/44 mitogen-activated protein kinase (MAPK) pathway as a regulator excitotoxic cell death and aberrant structural remodeling in the hippocampus. Traumatic brain injury-induced cell death and pathophysiological alterations in synaptic architecture are likely to be underlying events leading to profound, long-term, mental disability. Importantly, there is a fundamental unresolved question regarding the signaling pathway(s) that regulate brain injury-induced cell death and structural remodeling. Based on recent work by others, our published findings, and the preliminary data reported here, we propose that the MAPK pathway is both neuroprotective and couples excitotoxic stimuli to structural plasticity. To both test these hypotheses and begin to identify potential therapeutic approaches to target MAPK signaling, we have assembled a novel set of transgenic mice and an array of screening assays. In Aim 1, we will examine the role of the MAPK pathway as a regulator of cell viability. Importantly, the precise contribution of MAPK signaling to neuronal survival in vivo is not known. Along these lines, a number of in vitro studies have reported that MAPK signaling can either contribute to or attenuate neuronal death, depending on the experimental paradigm. In this aim, we will characterize the temporal and cell-type specific expression of status epilepticus-(SE) induced MAPK pathway activation in the hippocampus, and then determine whether MAPK signaling confers protection against SE-induced cell death. We will also test potential molecular mechanisms by which MAPK signaling modulates cell viability. In Aim 2, we will determine whether MAPK signaling couples excitotoxic stress to aberrant structural plasticity. A good deal of work has implicated the MAPK pathway as a regulator of developmentally-dependent dendrite and axon growth, however, the role of the MAPK pathway in pathophysiologically-induced structural remodeling has not been rigorously addressed. Given its robust reorganization, emphasis will be placed on the granule cell layer of the dentate gyrus. Our research will provide insights into the potential therapeutic value of targeting MAPK Signaling to avert traumatic brain injury cell-death and aberrant structural plasticity.